The present invention relates to a process and to a machine for spotting superficial defects on layers and in particular on sleeves of elastomeric material.
In the embodiment described hereinafter, the subject process and the subject machine are ready to be used in the qualitative verification sleeves having an axially tubular body that after passing quality control test, will be cut at a plurality of axially spaced points so as to produce a plurality of transmission belts, and more accurately toothed belts.
This does not, however, exclude the possibility of the use of the invention for spotting superficial defects on sleeves for belts of other types, such as, say, trapezoid-shaped or flat or grooved belts, or for spotting superficial defects on sleeves or other products of elastomeric material of a different type, such as, say, flexible hoses and rubber-coated panels.
As is known, in the production of transmission belts in general, there is first provided an axially elongated tubular sleeve, which is ready to be cut along several axially equidistantly spaced circumferential lines so as to obtain the separation of the individual belts.
This sleeve is made by winding in succession, on a suitable cylindrical matrix, one or more layers of elastomeric material combined with at least one layer of inextensible cords, circumferentially wound onto the matrix itself.
After these winding operations, the semi-finished product is coated with a protective sheet of paper or such like, to be subsequently subjected to a curing operation in an autoclave.
During the course of the curing operation the semi-finished product, which is first encased in a rubber chamber or coating sheath, is subjected to a combined action of heat and centripetal compression for example by steam under pressure, applied to the outside of the rubber sheath, forcing the rubber into the interstices of the reinforcement layers and takes the shape of teeth on the exterior surface of the matrix.
At the end of the curing operation the tubular sleeve obtained, previously removed from the autoclave and from the chamber or rubber sheath, must be subjected to a so-called "rasping" operation to remove the protective sheet of paper which was applied earlier so as to avoid, during the curing operation, that the elastomeric material in the uncured state might adhere to the rubber sheath. The rasping operation has the further object of evening out the sleeve's outer surface.
Before proceeding with the circumferential cutting operations to obtain the individual belts, it is important that the sleeve be subjected to some qualitative checks, to verify the possible presence of structural defects in the same.
One of these checks consists of identifying the possible presence of superficial irregularities which can be constituted, say, by fragments of paper not removed during the rasping step.
Other types of irregularities which can be found, are cuts, cracks or grooves localized on the surface of the sleeve, due, for example, to the seepage of steam or to other drawbacks which have occurred during the curing operation and/or during the course of processes prior to it.
The surface of the sleeve can also have local swellings due to the seepage of gases from inside the elastomeric material, or, in this case again, to the seepage of steam during the curing operation.
Lastly, it can occur that at certain points on the surface of the sleeve there are irregularities due to the presence of junction knots made on the inextensible cords during the course of the previous winding stage.
The methods currently in use to identify all these possible irregularities are substantially based on the visual examination of the surface of the sleeve on the part of an operator. It is evident, that the outcomes of such a check are entirely subjective, since they depend on the ability of the operator and on the attention he or she devotes to the execution of the check.